With the proliferation of computing devices around the world and their mainstream use for accessing the Internet, various alphanumerical data or text entry methods have been developed. Usually, alphanumeric data is entered via a keyboard or keypad device that includes keys for entering the letters of an alphabetical system. Keyboards are in use today that support the alphabetical system and letters of many languages, for example, English, French, Arabic, Japanese, Chinese, etc. For entering English letters, most keyboards use a well known “QWERTY” layout for positioning letters on the keys. The “QWERTY” layout was developed in the early days of mechanical typewriters, mainly to minimize mechanical jamming instances associated with typing English letters.
With the increased mobility of the users, the size of the computing devices has been decreasing steadily. Space limitation imposed by such decrease in size has created a challenge to design practical keypads that would fit on a small computing device, for example, a laptop or a PDA. Some small devices incorporate a full, but miniaturized QWERTY keypad to provide users with a familiar text entry system. Some of the miniaturized keypads, however, are so small that they must be used with the tip of one finger or even the sharp tip of a pen-like device.
Because limited keypad space on many small devices makes the use of a full keypad prohibitive or difficult, alternative text entry methods have been devised. For example, some PDA's like 3Com's Palm Pilot provide a handwriting-recognition system. With some training, users can input letters through defined pen strokes. However, entering letters using this system requires the use of both hands, which is unsuitable under some conditions, for example, while driving.
Today, many wireless devices (such as, cellular telephones) are also used for Internet browsing and instant messaging. Most wireless devices do not use a “QWERTY” keyboard or hand-writing recognition system. In general, the input system for such devices is based on a 12-key layout, with some having additional keys for special functions. As shown in FIG. 1, a conventional keypad consists of number keys 0-9 and two additional keys (# and *). Based on a rudimentary grouping, letters A-Z are spread over keys 2-9 in alphabetical order, where either three or four letters are assigned to a key.
Another class of solutions is based on virtual or soft-keyboards, where the size and positions of the keys can be arbitrarily defined to increase efficiency. With the popularity of Palm Pilots and the emergence of tablet and wearable computers this strategy has become of particular interest. Using virtual keyboards different keyboard configurations can be used to suit the task at hand or the language to be used.
The most commonly used text entry method for the 12-key layout is described in U.S. Pat. Nos. 5,392,338 and 4,658,417. The method is a multi-press method that requires activating a particular number-key once or several times until a desired letter is displayed. The method requires locating a desired letter, which is grouped among two or three other letters, on a corresponding number key. Once the corresponding number key is located, the user then activates the located key a number of times according to the position of that letter in the group of alphabets on the key. However, for sequential entry of two consecutive letters on the same key (for example, letters h and I, which are on key-4) the user, after entering a first letter on a key, must pause for a predefined time period (typically, two seconds) to enter a subsequent letter on the same key. The pause would allow the system to recognize the sequential entry of two letters on the same key. For example, to type the word “this” using the above described multi-press method, the user must activate the following sequence of keys:                Activate key (8TUV) once to enter letter t;        Activate key (4GHI) twice to enter letter h;        Pause for 2 seconds: since the next letter is on the same key;        Activate key (4GHI) three times to enter letter i;        Activate key (7PQRS) four times to enter letter s.        
It would be appreciated that the forced pause associated with entering letters that use the same key makes the data entry process slow, while interrupting the flow of user's input. To remedy this problem, some systems offer a time-out kill feature that allows the user to activate a stop-wait key (typically # key) to select the current choice and to allow the user to proceed with the next letter entry immediately. Although this feature eliminates the forced pause, it instead adds to the number of key entries.
Another conventional method for entering alphanumeric data using a 12-key layout is a two-key method, which is described in U.S. Pat. No. 4,650,927. To enter a particular letter under the two-key method, the user first activates the key where the letter is located, and then activates the number key indicating the position of the letter on that key. For example, to enter letter K, first key (5JKL) is pushed (since K is located on the numeric key 5) then key (2ABC) is pushed (since the K is the 2nd letter on the group JKL). To type the word “this” using the multi-press method, one must enter the following sequence of keys:                Activate key (8TUV) once, then activate key (1) once to enter letter t;        Activate key (4GHI) once, then activate key (2ABC) once to enter letter h;        Activate key (4GHI) once, then activate key (3DEF) once to enter letter i;        Activate key (7PQRS) once, then activate key (4GHI) once to enter letter s.        
Although this method does not suffer from the pause requirement of the multi-press method, in practice it has proved less popular, perhaps because it requires more user attentiveness, or because it forces the users to activate different keys more frequently.
Several other text entry systems using the 12-key layout have been proposed in the past. One early text entry method that uses a 12-key layout is described in U.S. Pat. No. 3,967,273. Although not widely used, the described method requires an array of keys with each key being labeled with at most a three by three array of letters. Text is entered by activating a first key on which a desired letter is located, and activating a second key as indicated by a position element of the desired letter on a position array disposed on the first key. This method maps the QWERTY letter pattern of the typewriter to the 12- or 16-key layout of a telephone for insuring those familiar with the location of letters and numbers on a typewriter can quickly find the letters on the keypad. There has been other alphanumeric data entry systems, proposed but rarely used, that relay on activating two keys to enter letters and special symbols. For example, U.S. Pat. Nos. 5,117,455 and 5,339,358 describe an arrangement for placing each letter or symbol between two keys. The sequence of activating the keys indicates the entry of that letter or symbol.
Other keypad input methods are described in U.S. Pat. Nos. 6,011,554, 5,664,896, and 4,650,927. Generally, these methods fall under a relatively new text entry technique known as the T9 technique. The T9 technique requires only one key activation per letter, and relies on a built-in linguistic model to disambiguate input on a word-by-word basis. One such method employs a disambiguation software that uses a dictionary and attempts to predict or “guess” the most probable word entry. This dictionary-based disambiguation relies on user attentiveness, since from time to time the user has to intervene and guide the software to select a less frequently used word, for example, abbreviation, jargon, foreign or otherwise words that are not in the dictionary. A similar method is described by Hedy Kober, Eugene Skepner, Terry Jones, Howard Gutowitz, and Scott MacKenzie, Linguistically Optimized Text Entry on a Cell Phone Submitted to CHI 2001. This method uses the probability of next letter occurrence as a guide to disambiguate and guess the letter to be input next.
Studies have been performed to assess the user entry speed for some of the above described methods. One study for predicting a potential expert user text entry speed is authored by Silfverberg, M., MacKenzie, I. S., & Korhonen, P, in Predicting text entry speeds on mobile phones, Proceedings of the ACM Conference on Human Factors in Computing Systems—CHI 2000, pp. 9-16. New York: ACM (2000). The study predicts text entry speed into the 12-key layout for one-handed thumb and two-handed index finger entry. According to the study, the traditional multi-press method can support text entry rates of up to about 25 wpm or 27 wpm for one-handed thumb input or two-handed index finger input, respectively, provided the user effectively employs the timeout kill feature for consecutive letters on the same key. If the timeout kill feature is not used to distinguish consecutive letters on the same key, then the entry rates is found to be decreased by about 4 wpm in each case. The two-key input technique is found to be slightly slower than the multi-press method (using timeout kill): 22 wpm and 25 wpm for one-handed thumb input and two-handed index finger input, respectively. Under the T9 technique, text entry rates of 41 wpm and 46 wpm are predicted for one-handed thumb input and two-handed index finger input, respectively. This study assumes expert behavior and a “perfect” disambiguation algorithm.
It is known that not all of the letters of an alphabetical system occur at the same frequency in a typical text. In the English alphabet, for example, letter E occurs most frequently (about 13% of the times) and letter Z appears least frequently (about 0.1% of the time). FIG. 2 depicts the frequency of occurrence of each letter of English alphabet. In the above described text entry methods, however, most frequently occurring letters often require more keystrokes than less-frequently-occurring letters. For example, according to the multi-press method, entry of letter E, the most-frequently-occurring letter, requires two activations of the key (3DEF), whereas entry of letter J, which appears only 0.2% of the times, requires only one activation of the key (5JKL). Using the multi-press method for entering a typical text of 1,000 letters, on the average, requires about 2,180 key activations. But if only the position of letters E and J were switched, on the average 128 fewer key activations would be needed, a saving of about 6% in the number of activations for the entire text. Likewise, to input letter S, which occurs 6% of the times, four activations of key (7PQRS) are required, but to enter P, which occurs 2.7% of the times, only one activation of key (7PQRS) is needed. It has been found that switching these two letters on the key would further reduce the number of activations by 5%.
Accordingly, the inefficient arrangement of the letters on the keys leads to a large number of unnecessary key activations, thereby increasing text entry time. Therefore, there exists a need for providing a keypad and a text entry method that is convenient to use, while increasing the speed by which text data is entered into a keypad.